This invention relates to a numerical control servo system which calculates a difference between a set numerical value and a measured numerical value corresponding to a controlled variable and performs a control based on the result of the calculation in a manner to reduce the difference to zero, and more particularly to a numerical control servo system which repeatedly carries out such a control.
In conventional types of numerical control servo systems, since the gain of a feedback control loop cannot be made infinity, a controlled deviation is produced. Therefore, for example, in the case where a number to be cut is fed by a predetermined length under the control of the numerical control servo system and cut into the predetermined length, an error corresponding to the abovesaid controlled deviation is introduced in the length of each severed member. In addition, the controlled deviation gradually changes with the lapse of time due to a drift of a digital-to-analog converter provided in the control system. This makes it impossible to set a numerical value in anticipation of the abovesaid controlled deviation, which results in a defect that the controlled deviation undergoes a gradual change.
An object of this invention is to provide a numerical control servo system which is capable of reducing the controlled deviation sufficiently small or to zero.